The present invention relates to the control of a hard disk drive having a dual stage actuator. In particular, the present invention relates to controlling the position of a dual stage actuator following a seek operation.
Computer disk drives store information on magnetic disks or platters. Typically, the information is stored on each disk in concentric tracks. The data tracks are usually divided into sectors. Information is written to and read from a disk by a transducer head. The transducer head may include a read head separate from a write head, or the read and write heads may be integrated into a single read/write head. The transducer head is mounted on an actuator arm capable of moving the transducer head radially over the disk. Accordingly, the movement of the actuator arm allows the transducer head to access different data tracks. The disk is rotated by a spindle motor at a high speed, allowing the transducer head to access different sectors within each track on the disk.
The actuator arm is interconnected to a motor or coarse actuator, such as a voice coil motor (VCM), to move the actuator arm such that the head moves radially over the disk. Operation of the coarse actuator is controlled by a servo control system. The servo control system generally performs two distinct functions: seek control and track following. The seek control function comprises controllably moving the actuator arm such that the transducer head is moved from an initial position to a target track position. In general, the seek function is initiated when a host computer associated with the computer disk drive issues a command to read data from or write data to a target track on the disk. Once the transducer head has been moved sufficiently close to the target track by the seek function of the control system, the track following function of the servo control system is activated to center and maintain the transducer head on the target track until the desired data transfers are completed.
Typically, the transducer head will oscillate about the center line of the target track for a period of time following the transition of the servo control system from the seek mode to the track following mode. This is known as settling. Because data written while the transducer head is oscillating about the center line of the track may be unrecoverable during subsequent attempts to read that data, write operations are typically prohibited for a period of time following a transition from the seek mode to the track following mode. In addition, because data from adjacent tracks may inadvertently be read, or may corrupt the read signal detected by the transducer head during read operations attempted while the transducer head is oscillating, read operations are also typically prohibited for a period of time following a transition from the seek mode to the track following mode. However, providing such settling times (i.e., times during which reading and writing by the transducer head is not allowed) decreases the performance of the disk drive by delaying read and write operations following a seek operation.
When the servo loop is switched to settling mode control after seeking, non-zero initial states in the plant cause oscillations of the transducer head. In order to decrease the amount of time during which the transducer head oscillates about a target track following a seek operation, various measures have been proposed and implemented. For example, initial value compensation has been applied to counteract the impulse signal that is introduced to the coarse actuator when the controller switches from the seek function to the track following function, or from the seek function to a specially provided settling function. However, only limited information regarding the parameters or plant states of the transducer head are available following a seek operation. For example, generally only position and velocity information is available. Provided with only information concerning the velocity and position of the transducer head, a system utilizing initial value compensation may be effective in reducing settling times. In particular, such systems may be effective in reducing the oscillation of the transducer head about a target track. However, further reductions in such oscillations are desirable. In addition, previous initial value compensation schemes have resulted in an oscillatory control effort being provided to the coarse actuator. This oscillatory control effort may, in some instances, result in a high frequency oscillation of the transducer head, and may produce an objectionable acoustical output.
The track following function of the servo control system generally comprises maintaining the transducer head at a desired position with respect to a track being followed (e.g., over a centerline of the track). Typically, the transducer head must be moved slightly during track following to maintain a desired position over the track. This is because, due to various factors, the track may appear to move beneath the transducer head. For example, the track may have been written so that it is not perfectly concentric about the axis of rotation of the disk. The apparent movement of the track with respect to the transducer head may also be caused by defects within the spindle bearing about which the disk rotates, or by random variations, such as may be caused by external shocks or other environmental influences. In addition, the transducer head itself may oscillate with respect to the track due to the vibration of the actuator arm and suspension.
The ability to precisely position a transducer head with respect to a track being followed has become increasingly important, as data and track densities in hard disk drives have increased. In particular, the space between adjacent tracks has become increasingly small, and the tracks themselves have become increasingly narrow. In order to increase the precision with which a transducer head may be positioned with respect to a track during track following, an articulated actuator arm may be used. In general, the angle of the distal portion, or second stage, of the actuator arm with respect to the main portion, or first stage, of the actuator arm is controlled by a microactuator. By operating the microactuator to introduce small changes in the position of the transducer head with respect to a track being followed, the accuracy of track following operations may be increased. However, because of the relatively small range of motion provided by microactuators, their range of motion is easily saturated. Accordingly, microactuators have previously only been employed during track following operations. In particular, microactuators have not been provided with an initial value compensation signal following a seek operation to improve the settling performance of a hard disk drive.
It would be advantageous to provide a computer hard disk drive with a decreased period of delay following seek operations. In particular, it would be advantageous to provide a computer disk drive having reduced settling times following a seek operation. In addition, it would be advantageous to provide a computer hard disk drive having a reduced acoustical output. Additionally, it would be desirable to provide a computer hard disk drive having reduced settling times and reduced acoustical output that is reliable in operation and that can be implemented at an acceptable cost.
In accordance with the present invention, a method and an apparatus for controlling a transducer head in a computer hard disk drive following a seek operation are provided. The present invention generally provides a control signal that includes an initial value compensation signal to both a coarse actuator and to a microactuator associated with an actuator arm following a seek operation. In particular, the present invention allows the microactuator to beneficially participate in the positioning of a transducer head immediately following a seek operation.
In accordance with an embodiment of the present invention, a method for controlling the position of a transducer head following a seek operation is provided. According to this embodiment, a signal that is representative of the initial plant states of the transducer head following the seek operation is passed through an initial value compensator to produce a compensation signal. The compensation signal is provided to first and second signal modifiers. A first signal from the first signal modifier is provided to a microactuator. A second signal from the second signal modifier is provided to a coarse actuator. The introduction of an initial value compensation signal dampens the initial impulse response experienced when the track following mode is entered. In addition, providing the compensation signal to both a microactuator and a coarse actuator improves the performance of the hard disk drive. In particular, oscillations are more effectively damped, decreasing the required settling time of the transducer head and decreasing the acoustical output of the hard disk drive.
According to another embodiment of the present invention, a hard disk drive having an improved transducer head settling scheme is provided. The disk drive includes a controller for providing control signals to a microactuator and a coarse actuator. The controller receives information regarding the initial plant states of the transducer head. An initial value compensation signal is the result of passing the signal concerning the initial plant states through an initial value compensator. The generated compensation signal is then provided to first and second signal modifiers. The first signal modifier provides a first control signal to the microactuator, and the second signal modifier provides a second control signal to the coarse actuator. By providing compensated signals to both a microactuator and a coarse actuator following a seek operation, the settling time of the transducer head decreases and the acoustical output of the hard disk drive decreases.
According to a further embodiment of the present invention, the first signal modifier multiplies the compensated signal by a first amount, and the second signal modifier multiplies the compensated signal by a second amount. According to still another embodiment of the present invention, the first and second signal modifiers include filters.
According to still another embodiment of the present invention, the first signal modifier is a high pass filter, and the second signal modifier is a low pass filter.
According to a further embodiment of the present invention, the microactuator is a piezoelectric actuator, an electromagnetic actuator, or an electrostatic actuator. The coarse actuator may be a voice coil motor.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. A method and an apparatus for controlling a transducer head in a computer hard disk drive following a seek operation are provided. In particular, a method and an apparatus in accordance with the present invention provide an initial value compensation signal to first and second actuators when the hard disk drive controller switches from a seek control function to a track following control function. Accordingly, the settling time of a hard disk drive in accordance with the present invention is improved. In addition, a hard disk drive in accordance with the present invention produces less acoustical noise after the controller transitions from seek control to track following control.